Insect Control: Horticultural Oils Fact Sheet No

Home , Neem oil

Insect Control: Horticultural Oils Fact Sheet No. 5.569 Insect Series|Home and Garden by W.S. Cranshaw and B. Baxendale* Various oils have been used for centuries Source of Spray Oils Quick Facts to control insect and mite pests. Oils remain Essentially all commercially available • Certain oils, diluted with water an important tool to manage certain pest horticultural oils (e.g., SunsprayR, ScalecideR, and applied as sprays, can problems (e.g., scales, aphids, mites) on fruit Volck R) are refined petroleum products also trees, shade trees and woody ornamental known as mineral oils. Impurities in the oil be effective controls of many plants. Several highly refined oils extend this that are associated with plant injury, such plant pests. usefulness to flowers, vegetables and other as aromatic compounds and compounds herbaceous plants. Oils also can control some • Horticultural oils are usually containing sulfur, nitrogen or oxygen, are highly refined petroleum oils plant diseases, such as powdery mildew. Oils removed. Filtration, distillation and dewaxing combined with an emulsifying used to protect plants have been called by complete the production of the finished base agent. Some plant-derived many names, but perhaps horticultural oils oil. Final formulations of horticultural oils best describes them as these are all oils used are normally combined with an emulsifying oils also are used. to control pests on plants. agent that allows the oil to mix with water. • Advantages of oils include Oils have different effects on pest insects. This mixture usually is used at about a 2 The most important is that they block safety, effectiveness and percent dilution. limited effects on beneficial the air holes (spiracles) through which Vegetable oils also can be used as insects. insects breathe, causing them to die from insecticides, although the type of oil can asphyxiation. In some cases, oils also may act greatly affect its activity. Cottonseed oil is • Do not use oils on certain as poisons, interacting with the fatty acids generally considered the most insecticidal sensitive plants. Plants under of the insect and interfering with normal of the vegetable oils. Soybean oil, the most metabolism. Oils also may disrupt how an drought stress may have commonly available vegetable oil used in increased risk of injury. insect feeds, a feature that is particularly cooking, has often provided fair to good important in the transmission of some plant control of some insects and mites. viruses by aphids. Extracts from seeds of the neem Oils pose few risks to people or to most tree (Azadirachta indica) have recently desirable species, including beneficial natural attracted attention as a source of pest enemies of insect pests. This allows oils management products. Several neem- to integrate well with biological controls. derived insecticides have been developed. Toxicity is minimal, at least compared A number of compounds found in neem to alternative pesticides, and oils quickly seeds, notably azadirachtin, have proven dissipate through evaporation, leaving useful as insecticides. However, the oil little residue. Oils also are easy to apply fraction of neem seed extracts, which is with existing spray equipment and can be mostly free of azadirachtin and related mixed with many other pesticides to extend terpenoid compounds, also has demonstrated their performance. effects as a fungicide and insecticide. At The main limitation of spray oils is their least one product currently on the market, small but real potential to cause plant injury TrilogyR, consists of a largely azadirachtin- (phytotoxicity) in some situations. Oils also free oil fraction of neem seed extracts. It is can stain some surfaces, particularly dark- formulated with an emulsifier and mixed colored house paints. Some of the highly with water at a concentration similar to refined spray oils can largely eliminate these horticultural oils (0.5 to 2.0 percent). Many problems if they are properly applied. © Colorado State University over-the-counter products sold in nurseries Extension. 2/99. Revised 12/13. that mention neem contain the oils of neem www.ext.colostate.edu *W.S. Cranshaw, Colorado State University Extension seed extracts. entomologist and professor, bioagricultural sciences and pest management; and B. Baxendale, Teikyo Loretto Heights University professor, botany, Denver. 12/2013 In recent years there has been a surge transmission are sometimes called “stylet Table 2. Plants that tend to be sensitive to oils. in the development and marketing of oils,” a reference to the piercing and sucking Black walnut essential oils derived from herbs and spices mouthparts (stylets) of aphids that transmit Cryptomeria (e.g. thyme, mint, cinnamon). Garlic and these viruses. Douglas-fir cedar oils also are now common products Oils also are useful against powdery Hickories Junipers and cedars on nurery shelves, although there has been mildew. Diluted horticultural oils, often Maples (particularly Japanese and red maple) little comparative testing. These appear to mixed with a small amount of baking soda, Redbud be effective as mineral oils. Some, notably can be an effective control for this common Smoke tree spruce) cinnamon oil, can have increased risk of plant disease. The neem oil products have Spruce (particularly dwarf Alberta The neem oil insecticides (TrilogyR) have causing plant injury. been effective against several types of been most widely used on greenhouse-grown powdery mildew and rust. ornamentals. They have shown good plant safety, but there are some precautions for use Insect and Mite Control on impatiens, fuschia, hibiscus, some roses, ornamental olive and some carnation varieties. Historically, the primary reason oils Precautions were developed was because of their The following precautions are effectiveness on otherwise hard-to-control recommended whenever using an oil on a Terms Used to pest problems on fruit trees. They were woody plant: used as a dormant-season application 1. Avoid using oils on plants that tend to Describe Oils (before bud swelling and bud break) to kill be oil-sensitive (Table 2). Avoid drift Dormant oil: An oil used on woody mites and insects, such as scales and aphids, onto sensitive plants. plants during the dormant season. This that spent the winter on the plant. Dormant 2. Do not apply when temperatures are term originally referred to heavier weight, oil applications also control certain excessively high (above 100 degrees less well-refined oils that were unsafe to overwintered shade tree pests. F) or low (below freezing). High use on plants after they broke dormancy. Recently, improvements in refining temperature limitations are primarily However, these older oils have been have produced oils with increased safety to related to the drought-stress status replaced with more refined, light-weight plants and thus expanded their potential of the plant. Plants under stress may oils that have potential application to uses (Table 1). Summer or foliar treatments be damaged. Those not stressed are plant foliage. Dormant oil now refers to are now possible for a variety of pests much less likely to be damaged by an the time of application rather than to any during the growing season. Oils also can be oil application. Dry conditions without characteristic type of oil. mixed with other insecticides, providing a plant stress generally reduce risk of Essential oil: A plant derivced oil that is broader spectrum and greater persistence injury by oil, because evaporation is ______(e.g., thymol, clove oil, mint of control. Spider mites, whiteflies and more rapid. oil). young stages of scales are common pests 3. Do not apply oils during freezing Horticultural oils: An oil used to that can be controlled by oils during the weather. This can cause the emulsion control a pest on plants. growing season. to break down and produce uneven Mineral oil: A petroleum-derived oil Oils are sometimes applied to prevent coverage. (as opposed to vegetable oils). transmission of viruses. Many viruses 4. Do not apply oils if plant tissues are Narrow-range oil: A highly refined spread by aphids (nonpersistent viruses), wet or rain is likely. These conditions oil that has a narrow range of distillation. as well as some that are mechanically inhibit oil evaporation. High humidity Narrow-range oils fall in the superior oil transmitted by people, can be inhibited by (above 90 percent) also may contribute classification. The terms may be used nearly oil applications. Oils used to inhibit virus to injury risk, while low humidity interchangeably. generally reduces it. Spray oil: An oil designed to be mixed Table 1. Some plant pests controlled by horticultural oils. 5. Do not spray when shoots are growing. with water and applied to plants as a spray Dormant Season Applications 6. Avoid treating plants during the for pest control. Aphids that curl leaves in spring fall until after winter hardening Summer oil: An oil used on plants Caterpillars that winter as eggs on the plant has occurred. Fall treatments when foliage is present (also called foliar (leafrollers, tent caterpillars) have sometimes caused increased oils). As with dormant oil, the term now Mites that winter on the plant (e.g., conifer- infesting species) susceptibility to winter injury. refers to the time an application is made Scale insects (e.g., pine needle scale, striped 7. Do not apply oils in combination with rather than to the properties of the oil. pine scale, Kermes scale, cottony maple sulfur or sulfur-containing pesticides Supreme oil: A term used to categorize scale) such as Captan or Karathane. They highly refined oils that distill at slightly Summer/Foliar Applications can react with oils to form phytotoxic higher temperatures and over a wider range Insects and Mites Adelgids compounds. Because elemental than the narrow-range oils. Most supreme Aphids sulfur can persist for long periods, oils meet the characteristics of a superior Eriophyid mites label directions on most oils prohibit oil. Leafhoppers Scale insects their use within 30 days of a sulfur Superior oil: A term originated by P.J. Spider mites application. Chapman in 1947 to categorize summer- Whiteflies Diseases Powdery mildew Some aphid-transmitted viruses use oils that met certain specifications. This included a high proportion of paraffinic hydrocarbons and purification that allowed year-round use without phytotoxicity. Since then, further developments have resulted in oils that distill over a narrow temperature range. Most superior oils are now better referred to as narrow-range oils. Vegetable oil: An oil derived from the seeds of some oil seed crop (e.g., soybeans, canola, cottonseed).

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